1. Field of the Invention
The present invention relates to an apparatus and a method for detecting a voltage of batteries used as a power source for an electric motor of a hybrid vehicle which incorporates the electric motor and a combustion engine together as a driving source thereof.
2. Description of the Related Art
An electric motor used as a driving source of an electric car is driven by a battery power supply in which there are a plurality of battery units in a series connection and each of the plurality of the battery units is composed of several low-voltage batteries in a series connection. In such a battery power supply, all of the batteries in the battery units are required to operate normally and at an equal voltage. Therefore, it is necessary to detect a voltage of each battery unit in which several batteries are combined to confirm that each battery is operating normally. The voltage of the battery unit is usually detected by means of a differential amplifier.
However, in the above-described battery power supply, the total voltage may be as high as about 400 V, so that the battery power supply is required to be in a floating state in which the circuitry is not electrically grounded. Therefore, the voltage of each battery unit is measured in the floating state, i.e., without being established against a ground potential, so that there is a possibility that the detected voltages may undergo substantial fluctuation. Particularly, the voltage of a battery power supply used as a driving source of a hybrid vehicle is normally supplied to an electric motor via an inverter so that the voltage of each battery unit may undergo an even greater fluctuation. A battery unit voltage which in itself undergoes a great fluctuation can not be accurately detected.
In one aspect of the invention, there is provided a voltage detection apparatus for detecting a voltage of at least one battery, including: capacitor means to which a voltage is applied from the at least one battery and in which an electric charge accumulates; adjustment means for adjusting potentials at both ends of the capacitor means such that a potential difference between a potential at one end of the capacitor means and a reference potential is less than a potential difference between a potential at one end of the at least one battery and the reference potential, and that a potential difference between a potential at another end of the capacitor means and the reference potential is less than a potential difference between a potential at another end of the at least one battery and the reference potential; and voltage detection means for detecting a voltage of the at least one battery based on a potential difference between the one end of the capacitor means and the other end of the capacitor means after the potentials of both ends of the capacitor means have been adjusted by the adjustment means.
In one embodiment of the invention, the capacitor means includes a plurality of capacitors in a series connection.
In another embodiment of the invention, the capacitor means is electrically connected with the at least one battery via a first switching means, the adjustment means includes a second switching means for switching a state of the capacitor means so as to be electrically coupled or decoupled to or from a prescribed potential, and the voltage detection means is electrically coupled to the capacitor means via a third switching means.
In still another embodiment of the invention, the capacitor means is electrically coupled to the prescribed potential via the second switching means, and the potentials at both ends of the capacitor means are adjusted.
In still another embodiment of the invention, a potential difference between the one end of the at least one battery and the other end of the at least one battery is equal to the potential difference between the one end of the capacitor means and the other end of the capacitor means.
In still another embodiment of the invention, the capacitor means includes a plurality of capacitors in a series connection and at least one node between the plurality of capacitors is coupled to the prescribed potential via the second switching means.
In still another embodiment of the invention, the voltage detection apparatus further includes a fourth switching means for switching a state of a first input terminal of the voltage detection means so as to be electrically coupled or decoupled to or from the reference potential.
In still another embodiment of the invention, the first input terminal is electrically coupled to the reference potential via the fourth switching means and a potential of the first input terminal is equal to the reference potential.
In still another embodiment of the invention, the voltage detection apparatus further includes conversion means for converting an analog signal from the voltage detection means to a digital signal.
In still another embodiment of the invention, the voltage detection means is a differential amplifier.
In another aspect of the invention, there is provided a method for detecting a voltage of at least one battery by means of the voltage detection apparatus, including the steps of: electrically coupling the at least one battery to the capacitor means via the first switching means so as to allow an electric charge to accumulate in the capacitor means; electrically isolating the at least one battery and the capacitor means from each other after the electric charge is accumulated in the capacitor means; electrically coupling the capacitor means to the reference potential via the second switching means, thereby adjusting the potentials at both ends of the capacitor means; electrically coupling the capacitor means to the voltage detection means via the third switching means; and detecting the potential difference between the one end of the capacitor means and the other end of the capacitor means by means of the voltage detection means.
In one embodiment of the invention, the voltage detection apparatus includes a fourth switching means for switching a state of a first input terminal of the voltage detection means so as to be electrically coupled or decoupled to or from the reference potential, the method further includes the steps of: electrically coupling the first input terminal to the reference potential via the fourth switching means; and switching a state of the first input terminal so as not to be electrically coupled to the reference potential via the fourth switching means after the step of electrically coupling the capacitor means to the voltage detection means.
In another embodiment of the invention, the step of adjusting the potentials at both ends of the capacitor means and the step of electrically coupling the first input terminal to the reference potential are performed simultaneously.
Thus, the invention described herein makes possible the advantages of providing a battery voltage detection apparatus which is capable of accurately measuring a voltage of a battery, and a method of detecting a voltage of a battery by means of the apparatus.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.